Fault (geology)

About: Fault (geology) is a research topic. Over the lifetime, 26732 publications have been published within this topic receiving 744535 citations.

Fault-propagation folding in extensional settings: Examples of structural style and synrift sedimentary response from the Suez rift, Sinai, Egypt

Abstract: Field data from the Oligocene–Miocene Gulf of Suez rift demonstrate that coeval growth faults, folds, and transfer zones exerted a major control on synrift stratigraphic sequence development. Growth folds in the Suez rift are related to steeply dipping normal faults that propagated upward, resulting in broad, upward-widening monoclines in overlying strata. Folding during fault propagation was accommodated by layer-parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault. The eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall. This evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments. Synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults, whereas they diverge into broadly synclinal expanded sections away from the growth monocline. Continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments, each successively younger sequence dipping basinward at a shallower angle than the previous one. The resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults. Along-strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low-relief transfer zones. Data from other rift basins indicate that fault-propagation folds are not unique to the Gulf of Suez.

Juxtaposition and Seal Diagrams to Help Analyze Fault Seals in Hydrocarbon Reservoirs

Abstract: A new set of diagrams aids in analyzing fault juxtaposition and sealing. The diagrams are based on the interaction of rock lithology and the fault displacement (throw) magnitude to control juxtapositions and fault seal types. The advantages of the diagrams are that they allow an evaluation of a fault seal without the need for detailed three-dimensional mapping of stratigraphic horizons and fault planes, and can be used to contour permeability, sealing capacity, and transmissibility of fault zones. These diagrams may be used to rapidly identify the critical fault throw and juxtapositions that require mapping to identify compartments in hydrocarbon reservoirs.

Fault parameters of the 1896 Sanriku Tsunami Earthquake estimated from Tsunami Numerical Modeling

Abstract: The June 15, 1896 Sanriku earthquake generated devastating tsunamis with the maximum run-up of 25 m and caused the worst tsunami disaster in the history of Japan, despite its moderate surface wave magnitude (Ms=7.2) and weak seismic intensity. This is a typical tsunami earthquake, which generates anomalously larger tsunamis than expected from its seismic waves. Previously proposed mechanisms of tsunami earthquakes include submarine slumping and slow rupture in the accretionary wedge or in the subducted sediments. In this paper, we estimate the fault parameters of the 1896 tsunami earthquake by numerically computing the tsunami and comparing the waveforms with those recorded at three tide gauge stations in Japan. The result indicates that the tsunami source is very close to the Japan trench and the fault strike is parallel to the trench axis. The fault width is about 50 km, suggesting that the tsunami earthquake is a slow rupture in the subducted sediments beneath the accretionary wedge.

Uplift and seismicity driven by groundwater depletion in central California

Abstract: Human-caused groundwater depletion in California’s San Joaquin Valley contributes to uplift of the surrounding mountains and may affect the stability of the San Andreas Fault. Through a combination of pumping, irrigation and evapotranspiration across the past 150 years, California's Central Valley has lost close to 160 km3 of groundwater. Colin Amos and co-authors use GPS measurements of vertical ground deformation to show that a broad zone of rock uplift surrounds the San Joaquin Valley, on the southern part of the Central Valley basin. The observed uplift closely matches the flexure predicted by a simple elastic model driven by current rates of water-storage loss within the valley. The authors suggest that such seasonal uplift of the Coast Ranges reduces the effective normal stress resolved on the adjacent San Andreas Fault, which may explain some of the annual modulation of seismicity observed in this area. They also infer that observed contemporary uplift of the southern Sierra Nevada, previously attributed to tectonic and/or mantle-derived forces, is partly a consequence of human-induced groundwater depletion. Groundwater use in California’s San Joaquin Valley exceeds replenishment of the aquifer, leading to substantial diminution of this resource1,2,3,4 and rapid subsidence of the valley floor5. The volume of groundwater lost over the past century and a half also represents a substantial reduction in mass and a large-scale unburdening of the lithosphere, with significant but unexplored potential impacts on crustal deformation and seismicity. Here we use vertical global positioning system measurements to show that a broad zone of rock uplift of up to 1–3 mm per year surrounds the southern San Joaquin Valley. The observed uplift matches well with predicted flexure from a simple elastic model of current rates of water-storage loss, most of which is caused by groundwater depletion3. The height of the adjacent central Coast Ranges and the Sierra Nevada is strongly seasonal and peaks during the dry late summer and autumn, out of phase with uplift of the valley floor during wetter months. Our results suggest that long-term and late-summer flexural uplift of the Coast Ranges reduce the effective normal stress resolved on the San Andreas Fault. This process brings the fault closer to failure, thereby providing a viable mechanism for observed seasonality in microseismicity at Parkfield6 and potentially affecting long-term seismicity rates for fault systems adjacent to the valley. We also infer that the observed contemporary uplift of the southern Sierra Nevada previously attributed to tectonic or mantle-derived forces7,8,9,10 is partly a consequence of human-caused groundwater depletion.